Nomenclature
The present invention provides composition of matter for novel mitosene analogues funtionalized at the N-2 nitrogen. The term mitosene is an abbreviation of the chemical name 2,3-dihydro-9-hydroxymethyl-6-methyl-1-H-pyrrolo[1,2a]indole-5,8-dione, carbamate (Webb, et. al. J. Am. Chem. Soc. 84, 3185 (1962)). The common name 2,7-diaminomitosene, for example, has amino groups at the 2 and 7 carbon positions of the mitosene structure as follows: ##STR1##
General Description of the Invention
Rationale for designing compounds of the present invention is an extension of the finding that the mitomycin C reductive activation product 2,7-diaminomitosene forms noncovalent bonds with deoxyribonucleic acid (DNA) (D. M. Peterson, Diss-Abstr-Int-B. 48, 2331 (1987)). The ideas of the actual conception were to create 2,7-diaminomitosene analogues which have the general structure: ##STR2## and are:
A) are prodrugs that release the cytotoxic 2,7-diaminomitosene, and/or
B) target release of the prodrug by glutathione cleavage of a disulfide bond or aminosulfenyl bond, or
C) target release of the prodrug through hydrolysis of an amide, ester or thiolester, or
D) take advantage of selective uptake of the mitosene analogue or prodrug through a polyamine, peptide, oligosaccharide or nucleotide transport system, or
E) have a functional group that enhances the binding of the agent to DNA such as an oligonuclotide, polypeptide, oligosaccharide or polyamine, or
F) have a functional group such as ethanethiol which could produce an additional toxic species (ethylene sulfide) upon prodrug activation by glutathione.
Since mechanisms of action are difficult to prove, utility of these compounds is based on their own empirical antitumor, antimicrobial and/or antiviral activity and not on whether or not the agents act by these particular mechanisms.
Advantages of the Present Invention
One advantage of these mitosenes versus mitomycin analogues is reduced general toxicity. Agents currently used to treat cancer like mitomycin C can be limited by their serious toxic side effects. Compounds which deliver 2,7-diaminomitosene without producing the quinone methide (see scheme below)--a potent alkylating species which results from reductive activation of mitomycin C--are expected to be less toxic. Attack by the quinone methide on various biological macromolecules within a cell (e.g. Nu1=an enzyme) can be toxic. Delivering 2,7-diaminomitosene without the requirement of going through the quinone methide intermediate should reduce prodrug toxicity. ##STR3##
Another potential advantage of the new mitosenes is reduced cell resistance. Current cancer drugs like mitomycin C can be limited by resistance. Drug resistance can occur when high levels of reduced glutathione are present. A proposed mechanism for resistance is nucleophilic trapping of the quinone methide agent (Nu1=glutathione) before 2,7-diaminomitosene and/or crosslinks can form. Properly selecting analogues that would release 2,7-diaminomitosene in the presence of high glutathione levels would avoid the mechanism for mitomycin resistance and actually take advantage of this property of resistant cells for targeted delivery of the agent. ##STR4##
Shown above is the potential to form two toxins which could be employed to adjust toxicity.
Comparison of Present Invention to Mitomvcin Analogues ##STR5##
A clear distinction of the present invention from mitomycin analogues is the presence of a double bond in the 9-9a position for the mitosene. Mitomycin analogues do not possess this double bond and are commonly known in the literature as mitosanes. An even more important distinction is a methylene group at C-1 of the 2,7-diaminomitosene analogues in contrast to an aziridine ring in the mitomycin analogues. Since the mitosene has a methylene, it does not have a suitable leaving group to generate the quinone methide. This inability to form the quinone methide is what gives the mitosene analogues their advantages of reduced toxicity and reduced resistance.
Certain compounds of the present invention contain the general moiety R.dbd.CH.sub.2 CH.sub.2 SSR' (ethyldisulfide groups) which the prior art teaches to attach to an oxygen or nitrogen in the C7 position of the mitosane structure (e.g. U.S. Pat. Nos. 4,866,180 and 5,103,018). In the present invention, the ethyldisulfide groups are attached to the N2 position instead of the N7 position and the resulting composition of matter is a mitosene structure instead of a mitosane structure. The mitosene structure will not form DNA crosslinks and hence is proposed to work by a unique mechanism from the mitosane which is not dependent on the R group.
Comparison of Present Invention to Mitosenes in Prior Art
Since 2,7-diaminomitosene, N-2 R.dbd.H, is disclosed in the open literature, it is not a patentable entity (M. Tomasz & R. Lipman, Biochemistry 20, 5056 (1981)). It (2,7-diaminomitosene) has also been shown to possess antimicrobial activity albeit less toxic than mitomycin C under the conditions it was tested (B. Iynegar, R. Dorr, N. Shipp & W. Remers, J. Med. Chem. 33, 253 (1990)). This result, however, could have been influenced by the positively charged amine on 2,7-diaminomitosene which would retard its bioavailability via decreased solubility across a hydrophobic membrane. Attachment of appropriate R groups described in the summary of the invention could increase hydrophobicity by masking the positively charged N-2 amine or facilitate uptake through a cellular transport system and hence increase bioavailability.
Other known 2,7-diaminomitosene derivatives of the general structure are the N-2 R.dbd.COCH.sub.3 (D. M. Peterson and J. Fisher, Biochemistry 25, 4077 (1986); M. Tomasz & R. Lipman, Biochemistry 20, 5056 (1981)) and N-2 R.dbd.CH.sub.3, SO.sub.2 CH.sub.3 or SO.sub.2 C.sub.6 H.sub.4 pCH.sub.3 (I. Han, D. J. Russell & H. Kohn, J. Org. Chem. 57, 1799 (1992)). These compounds (R.dbd.COCH.sub.3, CH.sub.3, SO.sub.2 CH.sub.3, and SO.sub.2 C.sub.6 H.sub.4 pCH.sub.3) were produced for chemical studies and are not implicated in their ability to act as antitumor agents. Since these structures are known, however, they are specifically excluded from the mitosene analogue descriptions below.
The general structure is also distinguished from the mitosene analogues which do not possess an amino group at N-2, and/or have an oxygen attached to the analogous C-1 position (M. Maliepaard, et. al., Anti-Cancer Drug Design, 7, 415-425 (1992) and U.S. Pat. No. 3,429,894 "Acetylated Mitosenes"). Moreover, these structures do not have the essential embodiment of a methylene group at C-1 which prevents the formation of a quinone methide. ##STR6##